Method of manufacturing a semiconductor device including a bump forming process

ABSTRACT

A method of manufacturing a semiconductor device includes an improved bump forming process. The bump forming process includes a bump forming step for forming a bump on the pad by feeding a gold wire from a capillary while moving the capillary; a sliding step of slightly moving the capillary in an almost horizontal direction after the formation of the bump to reduce the strength of the base portion of the gold wire connected to the bump; and a wire cutting step of cutting the gold wire at the base portion after the sliding step. In the sliding step, a moving speed of the capillary is made smaller than that in the bump forming step.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of manufacturing asemiconductor device including a process of forming a bump on a pad of asemiconductor chip.

2. Description of the Related Art

A method of weakening the base portion of a gold wire connected to abump after the bump is formed is disclosed in Japanese PatentApplication Laid-Open No. 5-235002. In this related art, a capillary ishorizontally moved after the formation of the bump, and the base portionof the gold wire connected to the bump is weakened. The weakening of thebase portion of the gold wire has an advantage of being able to makecutting of the gold wire easy.

However, when the capillary is to be horizontally moved after formationof the bump, and if the moving speed is set to be equal to the movingspeed of the capillary in the formation of the bump, then the shape andsize of the weakened base portion of the gold wire becomedisadvantageously unstable due to high moving speed of the capillary.When the base portion still has excessively high strength, although thebase portion is weakened, a projection extending upward is formed on thebase portion in cutting process, and mechanical impact in the cuttingprocess increases. At the moment the gold wire is cut, the gold wire fedfrom the capillary is bent and adversely affects a subsequent bondingoperation. On the other hand, when the base portion is excessivelyweakened, the bump and the gold wire are disconnected from each other inthe process of weakening. As a result, a gold wire cannot be fed fromthe capillary by a predetermined length for the next bonding operation.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method ofmanufacturing a semiconductor device in which the shape and size of thebase portion of a gold wire can be stabilized while the base portion ofthe gold wire is weakened.

According to one aspect of the present invention, a method ofmanufacturing a semiconductor device includes a bump forming process forforming a bump on a pad. The bump forming process comprises a bumpforming step, a sliding step and a cutting step. In the bump formingstep, a gold wire is fed from a capillary while moving the capillary ismoved to form a bump on the pad. In the sliding step, the capillary ismoved slightly in substantially horizontal direction after the formationof the bump to reduce the strength of the base portion of the gold wireconnected to the bump. In a cutting step, the gold wire is cut at thebase portion after the sliding step. Further, a moving speed of thecapillary in the sliding step is made smaller than that in the bumpforming step.

Other and further objects, features and advantages of the invention willappear more fully from the following description.

In the method of manufacturing a semiconductor device according to thepresent invention, after the bump forming step of forming a bump, in thesliding step of slightly moving the capillary in the almost horizontaldirection to reduce the strength of the base portion of the gold wireconnected to the bump, the moving speed of the capillary is set to besmaller than that in the bump forming step. For this reason, in thesliding step, a moving distance of the gold wire in substantiallyhorizontal direction is stabilized. Accordingly, the shape and size ofthe base portion of the gold wire connected to the bump are stabilized.An unnecessary projection can be prevented from being formed when thegold wire is cut at the base portion, and a hindrance to a subsequentbonding operation can be prevented.

BREF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing movement of a capillary in a bump formingprocess included in the method of manufacturing a semiconductor deviceaccording to a first embodiment of the present invention.

FIG. 2 is an enlarged graph showing the sliding step and the cuttingstep shown in GIG. 2.

FIG. 3 is a perspective view showing a bump and a gold wire connected tothe bump formed by a bump forming process in the first embodiment of thepresent invention.

FIG. 4 is a perspective view showing a bump formed by the bump formingprocess in the first embodiment of the present invention.

FIG. 5 is a graph showing cutting strength of the gold wire incomparison to the conventional technology.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described belowwith reference to the accompanying drawings.

First Embodiment

FIG. 1 is a graph showing movement of a capillary in a bump formingprocess included in the method of manufacturing a semiconductor deviceaccording to the present invention. The bump forming process is executedby using a known boding machine. The bonding machine includes acapillary CP having a center hole through which a gold wire is fed, adamper CL, and a ball forming means BF for forming a ball BA at the tipend of the gold wire fed from the capillary CP.

The bump forming process shown in FIG. 1 includes three steps, i.e., abump forming step BP, a sliding step SL, and a cutting step CT. Thesliding step SL and the cutting step CT among the three steps areenlarged and shown in FIG. 2. In the first embodiment, a gold wirehaving a diameter d of 24.5 μm is used.

FIGS. 1 and 2 show ten operations A to J of the capillary. The bumpforming step BP includes the six operations A, B, C, D, E, and F, andthe sliding step SL includes the four operations G, H, I, and J.

The bump forming step BP will be described below. The operation A inFIG. 1 is executed after a first bonding operation X1. In the firstbonding operation X1, a gold wire is fed from the center hole of thecapillary CP, the ball BA is formed at the tip end of the gold wire byusing the ball forming means BF, and the ball BA is pressed on one padof the semiconductor device. The ball forming means BF is, for example,means for generating arc discharge between the ball forming means BF andthe tip end of the gold wire. The heat of the arc discharge forms theball BA at the tip end of the gold wire. After the formation of theball, the capillary CP is located above one pad of a semiconductor chip.In this state, the capillary is moved down to the pad, and the ball BAis pressed on the pad. This operation presses the ball BA on the pad tocomplete the first bonding operation X1.

In the operation A, the capillary CP is raised by a predetermineddistance from the state, in which the ball BA is pressed on the pad bythe capillary CP, in preparation for the next second bonding operationX2 and a gold wire is fed from the capillary CP. Besides the operationA, an operation B is the operation for giving a rising angle of thecapillary CP. By the operations A and B, the capillary is movedobliquely upward for the second bonding operation by a distancedepending on a rising of the operation A.

In an operation C, the capillary CP is moved by a predetermined amountof offset, for the second bonding operation X2, to a position shiftedfrom the center of the ball BA bonded by the first bonding operation X1.In the operation C, the capillary CP is raised right upward. Subsequentto the operations A and B for moving the capillary CP obliquely upward,the capillary CP is raised right upward, so that the capillary CP ismoved to a position distanced from the center of the ball BA by thepredetermined amount of offset.

Subsequent to the operation C, an operation D circularly moves thecapillary CP and finely controls an amount of the gold wire feedconnected to the ball BA bonded on the pad by the first bondingoperation X1. The amount of feed of the gold wire finely controlled bythe operation D determines the height of a bump to be formed.

An operation E is to perform horizontal movement, performed after thefeeding of the gold wire, for finely controlling the end position of thecircular movement of the capillary CP by the operation D. With thisoperation, the amount of feed of the gold wire connected to the ball BAis finally controlled. An operation F sets the direction of the offsetin relation to the amount of offset obtained by the operation C. Theoperation F sets a predetermined angular direction in 360° angulardirections around the center of the ball BA bonded by the first bondingoperation.

By the operations A to F, the gold wire is fed to the ball BA bonded onthe pad by the first bonding operation X1. In the state where the goldwire is given a slack depending on an amount of feed, the second bondingoperation X2 is executed on the ball BA. Thus, the first and secondbonding operations X1 and X2 form a bump. The height of the bump isdependent on the height of the ball BA obtained by first bondingoperation and the amount of feed of the gold wire by the operations A toF. The gold wire is connected to a position shifted from the centerposition of the formed bump by the amount of offset generated by theoperation C, and the gold wire extends almost right above to penetratethe center hole of the capillary CP.

The operations A to F of the capillary CP in the bump forming step BPare executed such that a moving speed V0 of the capillary CP is set at500 (mm/sec) to 1000 (mm/sec). The moving speed V0 is considerably high.However, in order to efficiently perform a bonding process to asemiconductor chip, the moving speed V0 as such is generally employed.

Subsequent to the bump forming step BP, the sliding step SL is executedas a characteristic feature of the invention. The sliding step SLincludes operations G, H, I, and J in FIG. 2.

The operation G is executed first in the sliding step SL, and isexecuted subsequent to the bump forming step BP. The operation G pullsup the capillary CP being in contact with the bump to a position wherethe capillary CP is not in contact with the bump, i.e., a positionslightly distanced from the bump. In the operation G, more specifically,the capillary is raised right upward from the bump by a small diameterGd of 110 μm or less. Since the diameter d of the gold wire is 24.5 μm,the pulling distance Gd is 449% of the diameter d of the gold wire.Actually, a pulling distance Gd is preferably set at 10 to 20 μm (39.3%to 78.7% of the diameter d of the gold wire). More specifically, apulling distance Gd of 15 μm (59% of the diameter d of the gold wire) isset.

A moving speed Gv of the operation G is set to be ½ to {fraction (1/10)}of the moving speed V0 in the bump forming step BP. More specifically,the moving speed Gv is set at ½ of the maximum value 1000 (mm/sec) ofthe moving speed V0, i.e., 500 (mm/sec), to {fraction (1/10)} of theminimum value 500 (mm/sec) of the moving speed V0, i.e., 100 (mm/sec).

The operation H is a slide operation executed subsequent to theoperation G. In the slide operation H, the capillary CP is moved by aslight distance in the horizontal direction, i.e., a direction almostparallel to the surface of the pad while applying supersonic waves. Amoving distance Hd in the horizontal distance is 60% to 80% of thediameter D of the gold wire. That is, since the diameter d of the goldwire is 25.4 μm, the moving distance Hd is preferably set at 15.2 to20.3 μm. More specifically, 70% of the diameter d of the gold wire,i.e., 17.8 μm is set. An operation I indicates supersonic waves appliedto the capillary.

The moving speed Hv of the capillary CP in the slide operation H is setto be lower than the moving speed V0 in the bump forming step BP. Themoving speed Hv is preferably ½ to {fraction (1/25)} of the moving speedV0, and is preferably set at ½ of the maximum value of 1000 (mm/sec) ofthe moving speed V0, i.e., 250 (mm/sec), to {fraction (1/25)} of theminimum value of 500 (mm/sec), i.e., 20 (mm/sec). In this range, themoving speed Hv is set at {fraction (1/15)} of the moving speed V0,i.e., 66.7 (mm/sec) which is {fraction (1/15)} of the maximum value of1000 (mm/sec) of the moving speed V0 to {fraction (1/25)} of the movingspeed V0, i.e., 40 (mm/sec) which is {fraction (1/25)} of the minimumvalue 500 (mm/sec) of the moving speed V0. In fact, the moving speed Hvis set at {fraction (1/25)} of the maximum value of 1000 (mm/sec) of themoving speed V0, i.e., 40 (mm/sec).

An operation J sets a moving direction of the capillary in the operationH, i.e., a specific direction in 360° horizontal directions in which thecapillary is moved.

In the sliding step SL, after the capillary CP is pulled up by thepulling distance Gd in the operation G, the capillary CP is horizontallymoved in the slide operation H by the moving distance Hd at the movingspeed Hv lower than the moving speed V0 of the capillary CP in the bumpforming step BP. With the horizontal movement of the capillary CP, thecapillary CP reduces the horizontal thickness of the base portion of thegold wire by horizontally pressing the base portion of the gold wireconnected to the bump and extended right downward from the central holeof the capillary CP.

For example, in the first embodiment, a gold wire having a diameter of25.4 μm is used, and the capillary CP is moved by the horizontal movingdistance Hd which is 70% the diameter, i.e., 17.8 μm. In this case, thehorizontal thickness of the base portion of the gold wire is simplyreduced to 25.4−17.8=7.6 μm. The reduction in thickness of the baseportion reduces the mechanical strength of the base portion of the goldwire.

In the slide operation H, supersonic vibration is applied to thecapillary CP. The supersonic vibration reduces the friction between thecapillary CP and the gold wire extending through the center hole of thecapillary CP in the slide operation H to a proper value. With thesupersonic vibration, the capillary CP horizontally smoothly presses thebase portion of the gold wire without causing the gold wire to jam inthe capillary CP, so that the thickness of the base portion is reduced.

FIG. 3 shows a bump and a gold wire connected to the bump on the finalstage of the sliding step SL. In FIG. 3, a bump 1 is formed on a pad 4.The gold wire 2 is connected to the bump 1 via its base portion 3. Theupper surface of the bump 1 is made flat by the pressure produced by thecapillary CP. A gold wire 2 is connected to the end portion on the uppersurface of the flattened bump 1 through a base portion 3. The horizontalthickness of the base portion 3 is sufficiently smaller than thediameter of the gold wire 2 to reduce the mechanical strength of thebase portion 3.

Since the horizontal moving speed Hv of the capillary CP in the slidingstep SL is set to be smaller than the operation speed V0 of thecapillary CP in the bump forming step BP, the moving distance of thecapillary CP is always stable in the slide operation H. As a result, thethickness of the base portion 3 is stabilized, the reduction in strengthbecomes stable, and the base portion 3 is weakened to have almostuniform strength.

In contrast, when the moving speed Hv in the slide operation H is set tobe equal to the operation speed V0, an acceleration generated by slighthorizontal movement in the slide operation H is large. The largeacceleration causes the following inconvenient cases. That is, the endposition of horizontal movement is unstable not to reduce the horizontalthickness of the base portion 3 to a predetermined thickness, or thethickness of the base portion 3 becomes zero to cut the gold wire. Whenthe base portion 3 is left thick, a projection extending upward isdisadvantageously left when cutting the base portion 3 in the nextcutting step CT. When the base portion 3 is cut by the slide operationH, the gold wire cannot be fed from the capillary CP and a tail portioncannot be secured before the next cutting step CT. A hindrance may occurto the subsequent bonding operation.

Subsequent to the sliding step SL, the cutting step CT of the gold wire2 is executed. Before the cutting step CT, an operation of pulling thecapillary CP immediately upward by a predetermined distance, e.g., 500to 600 μm, is performed. This operation secures a tail portion TP of thegold wire 2. This operation is executed when the gold wire 2 isconnected to the bump 1 at the base portion 3. More specifically, thecapillary CP is pulled upward when the gold wire 2 is connected to thebump 1, and the gold wire is fed from the capillary CP by apredetermined length. Thus, a tail portion having a predetermined lengthis secured. In the state in which the tail portion TP is secured, thegold wire 2 is clamped by a clamp means. In the state in which the goldwire 2 is clamped, and when the capillary CP is pulled upward, the goldwire is cut at the base portion 3. Resultantly, the tail portion TPextends from the capillary CP by a predetermined length. The clamp meansdoes not operate until the cutting step CT is started, and the clampmeans clamps the gold wire for the first time in the cutting step CT.

FIG. 4 shows a bump obtained after the cutting step CT is completed. Thegold wire is cut at the base portion 3, and a small extending portion 5is formed. The small extending portion 5 horizontally slightly extendsfrom the end portion of the upper surface of the bump 1, and will nothinder the subsequent bonding operation for the bump 1. The bump 1itself shown in FIG. 4 can also be used for connection to other circuit.Alternatively as will be describe in the second embodiment, reversebonding may be further performed, so that the bump 1 can be used forconnection to an inner lead.

FIG. 5 includes graphs showing cutting strengths of the gold wire in thecutting step CT. A graph Y1 indicates a cutting strength obtained in thefirst embodiment, and a graph Y2 indicates a cutting strength obtainedwhen the sliding step SL is not performed to compare the cuttingstrengths with each other. The ordinate indicates a cutting strength[gram force (gf)]. The graphs Y1 and Y2 indicate cutting strengthsobtained by using a gold wire having a diameter of 25.4 μm. However, inthe first embodiment, since a horizontal moving distance Hdcorresponding to 70% of the diameter is given, the cutting strengthconsiderably decreases.

After the cutting step CT, a ball BA is formed again at the lower end ofthe tail portion TP of the gold wire fed from the capillary CP by apredetermined length. The ball BA is formed by a ball forming means andused in the next bonding. In the first embodiment, the horizontalthickness of the base portion 3 is secured in the sliding step SL. As aresult, the tail portion TP having a predetermined length is secured, sothat the ball BA can be formed without any hindrance.

The features and advantages of the first embodiment may be summarized asfollows. As described above, in the first embodiment, after the bump 1is formed by the bump forming step BP, the sliding step SL is performedin which the capillary CP is horizontally slightly moved to reduce thestrength of the base portion 3 of the gold wire 2 connected to the bump1, and the moving speed of the capillary CP in the sliding step SL ismade lower than that in the bump forming step BP. For this reason, thesubstantially horizontal moving distance Hd in the sliding step SL canbe stabilized. Accordingly, the horizontal thickness of the base portion3 can be stabilized, and the strength of the base portion 3 can be setat a reduced value. Therefore, a stable bonding operation can beperformed.

Since the moving speed Hv of the capillary CP in the sliding step SL isreduced to ½ to {fraction (1/25)} of the operation speed V0 in the bumpforming step BP, preferably, {fraction (1/15)} to {fraction (1/25)} ofthe operation speed V0, the substantially horizontal moving distance Hdin the sliding step SL can be sufficiently stabilized.

The substantially horizontal moving distance Hd of the capillary CP inthe sliding step SL is set at 60 to 80%, particularly, 70%, of thediameter d of the gold wire. For this reason, the base portion 3 canobtain a required strength.

Since supersonic vibration is applied to the capillary CP in the slidingstep SL, the capillary CP can be smoothly and stably moved by apredetermined moving distance Hd in an almost horizontal direction.

Further in the sliding step SL, before the capillary CP is almosthorizontally moved, the capillary CP is raised in an almost verticaldirection such that the capillary CP is distanced from the bump. Forthis reason, when the capillary CP is almost horizontally moved, thecapillary CP can be smoothly and stably moved by the predeterminedmoving distance Hd without being caught by the bump 1.

Further, in the first embodiment, after the sliding step SL, in a statein which the gold wire 2 is connected to the bump 1, the capillary CP israised, and the gold wire is fed from the capillary CP by apredetermined length. For this reason and owing to the stabilized baseportion, the feeding of the gold wire from the capillary CP can beexecuted without any hindrance.

In addition, since the ball BA is formed on the end portion of the goldwire fed from the capillary CP, the ball BA having a predetermined sizecan be formed on the end portion of the gold wire having a predeterminedlength.

Second Embodiment

In the second embodiment, a bump 1 is formed by the method according tothe first embodiment, and a gold wire 2 is cut at a base portion 3.Thereafter, the gold wire is fed by a predetermined length from thecapillary CP, and a ball BA is formed on the end portion of the goldwire. In this state, ball bonding is performed to an inner lead of asemiconductor device by using the formed ball BA, and a reverse bondingstep is executed in which the gold wire extending from the ball-bandedlead is stitch-bonded on the bump.

In the ball banding, the ball BA formed on the tip end of the gold wireis bonded on the surface of an inner lead by the capillary CP. As iswell known, the inner lead is arranged around a semiconductor chip. Whenthe semiconductor chip is sealed by a resin package or the like, theinner lead is extended out of the resin package and electricallyconnected to an external circuit. From the ball bonding position, thegold wire is drawn on the upper surface of the bump 1 formed in a manneras described in the first embodiment, and is stitch-bonded on the uppersurface of the bump 1. After the stitch bonding, the gold wire is cut ata position where the stitch bonding is performed. The gold wireextending from the ball-bonded lead to the position where the stitchbonding is performed electrically connects the inner lead to the bump onthe semiconductor chip.

In the second embodiment, a predetermined relationship is kept between adirection from the inner lead to the bump and a direction of anoperation F in a bump forming step BP, or a direction of an operation Jin a sliding step SL. In the operation F, the direction of an offset isfrom the center of the ball BA bonded on a pad 4 by a first bondingoperation X1, i.e., in 360° directions around the center of the ballbonded on the pad by the first bonding operation X1. This direction ofoffset is set to be almost equal to a direction from the inner lead tothe bump. In the operation J, a moving direction is set in which thecapillary CP is almost horizontally moved in the sliding step SL. As inthe operation F, the direction is set to be almost equal to thedirection from the inner lead to the bump.

In the second embodiment, the direction of the offset performed by theoperation F and the direction of almost horizontal movement performed bythe operation J are set to be almost equal to the direction from theinner lead to the bump. As a result, the base portion 3 is connected tothe bump 1 at an end portion of the bump 1 on the opposite side of theinner lead. Furthermore, a slide operation G presses the base portion 3in such a direction that the base portion 3 is distanced from the innerlead, and the extending portion 5 obtained by a cutting step CT is alsoleft on the opposite side of the inner lead.

With this configuration, the gold wire extending from the inner lead tothe bump is easily stitch-bonded on the upper surface of the bump 1, andthe joining properties between the gold wire and the bump 1 areimproved.

The method of manufacturing a semiconductor device according to thepresent invention is applied to manufacturing of a semiconductorintegrated circuit or the like. The method is effectively used to form abump having a stable shape and a stable size on a pad of a semiconductorintegrated circuit.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay by practiced otherwise than as specifically described.

The entire disclosure of a Japanese Patent Application No. 2003-345470,filed on Oct. 3, 2003 including specification, claims, drawings andsummary, on which the Convention priority of the present application isbased, are incorporated herein by reference in its entirety.

1. A method of manufacturing a semiconductor device including a bumpforming process for forming a bump on a pad, said bump forming processcomprising: a bump forming step for feeding a gold wire from a capillarywhile moving said capillary to form a bump on said pad; a sliding stepof slightly moving said capillary in substantially horizontal directionafter the formation of said bump to reduce the strength of said baseportion of said gold wire connected to said bump; and a cutting step ofcutting said gold wire at said base portion after said sliding step,wherein a moving speed of said capillary in said sliding step is madesmaller than that in said bump forming step.
 2. The method ofmanufacturing a semiconductor device according to claim 1, wherein saidmoving speed of the capillary in said sliding step is set at ½ to{fraction (1/25)} of said moving speed of said capillary in said bumpforming step.
 3. The method of manufacturing a semiconductor deviceaccording to claim 2, wherein said moving speed of said capillary insaid sliding step is set at {fraction (1/15)} to {fraction (1/25)} ofsaid moving speed of said capillary in said bump forming step.
 4. Themethod of manufacturing a semiconductor device according to claim 1,wherein said capillary is substantially horizontally moved in saidsliding step by a moving distance of 60% to 80% of a diameter of saidgold wire.
 5. The method of manufacturing a semiconductor deviceaccording to claim 4, wherein said capillary is substantiallyhorizontally moved in said sliding step by a moving distance of issubstantially 70% of a diameter of said gold wire.
 6. The method ofmanufacturing a semiconductor device according to claim 1, whereinsupersonic vibration is applied to said capillary in said sliding stepwhen said capillary is substantially horizontally moved.
 7. The methodof manufacturing a semiconductor device according to claim 1, whereinsaid capillary is substantially vertically raised slightly to bedistanced from said bump before said capillary is substantiallyhorizontally moved in said sliding step.
 8. The method of manufacturinga semiconductor device according to claim 1, wherein said capillary israised with said gold wire being fed from said capillary by apredetermined length and wire cutting is executed in said cutting step.9. (Cancelled)
 9. The method of manufacturing a semiconductor deviceaccording to claim 8, wherein, after said cutting step, a ball is formedon an end portion of said gold wire fed from said capillary.
 10. Themethod of manufacturing a semiconductor device according to claim 9,further including, after forming said ball, a step of ball-bonding thegold wire on an inner lead and then stitch-bonding the gold wire ontosaid bump.
 11. The method of manufacturing a semiconductor deviceaccording to claim 10, wherein, in said sliding step, said capillary isslightly moved in a direction from said inner lead to said bump.